Autonomous vehicle ranging system with polarized antenna

ABSTRACT

A front end of a radar system is provided with a first front end apparatus and a second front end apparatus. A first transmit planar component and a first receive planar component in the first front end apparatus are arranged to be perpendicular to one another. A second transmit planar component and a second receive planar component in the second front end apparatus are arranged to be perpendicular to one another. A linear array of antennas is located along a second end of each planar component. Polarization of a first set of waves transmitted from the linear array of antennas of the first transmit planar component and polarization of a second set of waves transmitted from the linear array of antennas of the second transmit planar component are perpendicular to one another.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional PatentApplication No. 63/032,999, filed Jun. 1, 2020; U.S. Provisional PatentApplication No. 63/033,023, filed Jun. 1, 2020; U.S. Provisional PatentApplication No. 63/033,035, filed Jun. 1, 2020; U.S. Provisional PatentApplication No. 63/034,675, filed Jun. 4, 2020; U.S. Provisional PatentApplication No. 63/034,729, filed Jun. 4, 2020; U.S. Provisional PatentApplication No. 63/034,751, filed Jun. 4, 2020; U.S. Provisional PatentApplication No. 63/034,769, filed Jun. 4, 2020; and U.S. ProvisionalPatent Application No. 63/034,937, filed Jun. 4, 2020. The entirecontents and disclosure of these applications are incorporated byreference herein.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to apparatus and methods of detectingobjects or obstacles and, more particularly, apparatus and methods ofdetecting or recognizing objects or obstacles with high accuracy.

Description of the Related Art

A phased array radar system may be a radar system that manipulates thephase of one or more radio waves transmitted by a transmitting andreceiving module and uses a pattern of constructive and destructiveinterference created by the radio waves transmitted with differentphases to steer a beam of radio waves in a desired direction.

In modern radar systems, in order to achieve superior resolution andrange, it is desirable to maintain a broad bandwidth with minimal lossesthroughout the system. Moreover, the growing focus toward imaging radarsystems is pushing the frequency range for phased array systems into themillimeter-wave range and beyond. However, achieving a constantprogressive phase shift between adjacent antennas over a wide bandwidthis a significant challenge at millimeter-wave frequencies.

SUMMARY OF THE INVENTION

In one example embodiment, a front end of a radar system comprises afirst front end apparatus and a second front end apparatus. The firstfront end apparatus includes a first transmit planar component and afirst receive planar component. The first transmit planar component andthe first receive planar component are arranged to be perpendicular toone another. The second front end apparatus includes a second transmitplanar component and a second receive planar component. The secondtransmit planar component and the second receive planar component arearranged to be perpendicular to one another. Each of the first transmitplanar component, the first receive planar component, the secondtransmit planar component and the second receive planar componentincludes a first end, a second end, a cavity space and a linear array ofantennas. The second end is located opposite the first end.Electromagnetic waves propagate in propagation directions between thefirst end and the second end. The cavity space is bounded by beam portsalong a first side of the cavity space and by array ports along a secondside of the cavity space. The cavity space is in operative communicationwith the beam ports and with the array ports to form a Rotman lens. Thelinear array of antennas is located along the second end of the planarcomponent. Each of the antennas is in operative communication with acorresponding one of the array ports. The first transmit planarcomponent and the second transmit planar component are parallel to oneanother, and the first receive planar component and the second receiveplanar components are parallel to one another. A first set of waves aretransmitted from the linear array of antennas of the first transmitplanar component to be received by the linear array of antennas of thefirst receive planar component, and a second set of waves aretransmitted from the linear array of antennas of the second transmitplanar component to be received by the linear array of antennas of thesecond receive planar component. Polarization of the first set of wavestransmitted from the linear array of antennas of the first transmitplanar component and polarization of the second set of waves aretransmitted from the linear array of antennas of the second transmitplanar component are perpendicular to one another.

In another embodiment, a method of detecting an object, the methodcomprises: providing a first linear array of transmit antennas and asecond linear array of transmit antennas, the first linear array oftransmit antennas and the second linear array of transmit antennas beingparallel to one another; providing a first linear array of receiveantennas and a second linear array of receive antennas, the first lineararray of receive antennas and the second linear array of receiveantennas being parallel to one another; arranging the first linear arrayof transmit antennas and the first linear array of receive antennas tobe perpendicular to one another; arranging the second linear array oftransmit antennas and the second linear array of receive antennas to beperpendicular to one another; phase-shifting first waves by propagatingthe first waves through a first Rotman lens that is in operativecommunication with the first linear array of transmit antennas;phase-shifting second waves by propagating the second waves through asecond Rotman lens that is in operative communication with the secondlinear array of transmit antennas; transmitting the first waves throughthe first linear array of transmit antennas; transmitting the secondwaves through the second linear array of transmit antennas; receivingthe first waves reflected by an object through the first linear array ofreceive antennas; receiving the second waves reflected by an objectthrough the second linear array of receive antennas; propagating thefirst waves reflected by an object through a third Rotman lens that isin operative communication with the first linear array of receiveantennas; and propagating the second waves reflected by an objectthrough a fourth Rotman lens that is in operative communication with thesecond linear array of receive antennas.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 shows a schematic representation of an example embodiment of aradar system including a first front end apparatus and a second frontend apparatus in accordance with the present disclosure;

FIG. 2 shows an example embodiment of transmit modules and receivemodules of the first front end apparatus and the second front endapparatus;

FIG. 3 shows an example embodiment of transmit planar components andreceive planar components for the first and second front endapparatuses;

FIG. 4 shows an example embodiment of half blocks of the transmit planarcomponents and half blocks of the receive planar components wherewaveguides and a Rotman lens are formed thereon;

FIG. 5 is a close-up view of an example embodiment of a polarizationrotator on the half block of the transmit planar component;

FIG. 6 is an isolated view of the example polarization rotator includinga first section, an iris section and a second section;

FIG. 7A is a cross-sectional view across the first section of thepolarization rotator of a planar component;

FIG. 7B is a schematic representation of polarization of waves in thefirst section of the polarization rotator;

FIG. 8A is a cross-sectional view across the iris section of thepolarization rotator of the planar component;

FIG. 8B is a schematic representation of polarization of waves in theiris section of the polarization rotator;

FIG. 9A is a cross-sectional view across the second section of thepolarization rotator of a planar component;

FIG. 9B is a schematic representation of polarization of waves in thesecond section of the polarization rotator;

FIG. 10 shows an example embodiment of a front end where a Rotman lensand a transmission lines are formed with microstrips;

FIG. 11 shows an example embodiment of a half block of a planarcomponent for a front end device including a Rotman lens with sidewallabsorbers;

FIG. 12 shows a computer graphic illustration of an example embodimentof a fixture to test performance of a sidewall absorber;

FIG. 13 is a graph showing the minimum reflection (S11) and the maximaltransmission (S12) for the iris section for given dimensions of the irissection; and

FIG. 14 is an illustration of reflections around example triangularteeth of sidewall absorbers of the Rotman lens.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Range-finding systems use reflected waves to discern, for example, thepresence, distance and/or velocity of objects. Radio Detection AndRanging (radar) and other range-finding systems have been widelyemployed in applications, by way of non-limiting example, in autonomousvehicles such as self-driving cars, as well as in wirelesscommunications modems of the type employed, such as in Massive-MIMO(multiple-in-multiple-out) networks, 5G wireless telecommunications, allby way of non-limiting example.

The radar system may include optimized RF front-end device(s) aiding inachieving higher resolution by improving azimuth resolution, elevationresolution, or any combination thereof. Azimuth resolution is theability of a radar system to distinguish between objects at similarrange but different bearings. Elevation resolution is the ability of aradar system to distinguish between objects at similar range butdifferent elevation. Angular resolution characteristics of a radar aredetermined by the antenna beam-width represented by the −3 dB anglewhich is defined by the half-power (−3 dB) points. In some embodiments,radar system or phased array system disclosed herein may have a −3 dBbeam-width of 1.5 degree or less in both azimuth resolution andelevation resolution. In particular, the radar system can be configuredto achieve finer azimuth resolution and elevation resolution byemploying an RF front-end device having two linear antennas arraysarranged perpendicularly and a Rotman lens as a phase shifting network,as will be described below.

FIG. 1 shows a schematic illustration of an example radar system 100having the abovementioned functionalities. The radar system 100 mayinclude a millimeter wave radar that emits a low power millimeter waveoperating at 76-81 GHz (with a corresponding wavelength of about 4 mm).The radar system can also operate at other frequency range that is below76 GHz or above 81 GHz. The radar system may comprise any one or moreelements of a conventional radar system, a phased array radar system, anAESA (Active Electronically Scanned Array) radar system, a syntheticaperture radar (SAR) system, a MIMO (Multiple-Input Multiple-Output)radar system, and/or a phased-MIMO radar system. A conventional radarsystem may be a radar system that uses radio waves transmitted by atransmitting antenna and received by a receiving antenna to detectobjects. A phased array radar system may be a radar system thatmanipulates the phase of one or more radio waves transmitted by atransmitting and receiving module and uses a pattern of constructive anddestructive interference created by the radio waves transmitted withdifferent phases to steer a beam of radio waves in a desired direction.

The radar system 100 may be provided on a movable object to sense anenvironment surrounding the movable object. Alternatively, the radarsystem may be installed on a stationary object.

A movable object can be configured to move within any suitableenvironment, such as in air (e.g., a fixed-wing aircraft, a rotary-wingaircraft, or an aircraft having neither fixed wings nor rotary wings),in water (e.g., a ship or a submarine), on ground (e.g., a motorvehicle, such as a car, truck, bus, van, motorcycle, bicycle; a movablestructure or frame such as a stick, fishing pole; or a train), under theground (e.g., a subway), in space (e.g., a spaceplane, a satellite, or aprobe), or any combination of these environments. The movable object canbe a vehicle, such as a vehicle described elsewhere herein. In someembodiments, the movable object can be carried by a living subject, ortaken off from a living subject, such as a human or an animal.

In some cases, the movable object can be an autonomous vehicle which maybe referred to as an autonomous car, driverless car, self-driving car,robotic car, or unmanned vehicle. In some cases, an autonomous vehiclemay refer to a vehicle configured to sense its environment and navigateor drive with little or no human input. As an example, an autonomousvehicle may be configured to drive to any suitable location and controlor perform all safety-critical functions (e.g., driving, steering,braking, parking) for the entire trip, with the driver not expected tocontrol the vehicle at any time. As another example, an autonomousvehicle may allow a driver to safely turn their attention away fromdriving tasks in particular environments (e.g., on freeways), or anautonomous vehicle may provide control of a vehicle in all but a fewenvironments, requiring little or no input or attention from the driver.

In some instances, the radar systems may be integrated into a vehicle aspart of an autonomous-vehicle driving system. For example, a radarsystem may provide information about the surrounding environment to adriving system of an autonomous vehicle. An autonomous-vehicle drivingsystem may include one or more computing systems that receiveinformation from a radar system about the surrounding environment,analyze the received information, and provide control signals to thevehicle's driving systems (e.g., steering wheel, accelerator, brake, orturn signal).

The radar system 100 that may be used on a vehicle to determine aspatial disposition or physical characteristic of one or more targets ina surrounding environment. The radar system may advantageously have abuilt-in predictive model for object recognition or high-level decisionmaking. For example, the predictive model may determine one or moreproperties of a detected object (e.g., materials, volumetriccomposition, type, color, etc.) based on radar data. Alternatively oradditionally, the predictive model may run on an external system such asthe computing system of the vehicle.

The radar system may be mounted to any side of the vehicle, or to one ormore sides of the vehicle, e.g. a front side, rear side, lateral side,top side, or bottom side of the vehicle. In some cases, the radar systemmay be mounted between two adjacent sides of the vehicle. In some cases,the radar system may be mounted to the top of the vehicle. The systemmay be oriented to detect one or more targets in front of the vehicle,behind the vehicle, or to the lateral sides of the vehicle.

A target may be any object external to the vehicle. A target may be aliving being or an inanimate object. A target may be a pedestrian, ananimal, a vehicle, a building, a sign post, a sidewalk, a sidewalk curb,a fence, a tree, or any object that may obstruct a vehicle travelling inany given direction. A target may be stationary, moving, or capable ofmovement.

A target object may be located in the front, rear, or lateral side ofthe vehicle. A target object may be positioned at a range of about 1, 2,3, 4, 5, 10, 15, 20, 25, 50, 75, or 100 meters from the vehicle. Atarget may be located on the ground, in the water, or in the air. Atarget object may be oriented in any direction relative to the vehicle.A target object may be orientated to face the vehicle or oriented toface away from the vehicle at an angle ranging from 0 to 360 degrees.

A target may have a spatial disposition or characteristic that may bemeasured or detected. Spatial disposition information may includeinformation about the position, velocity, acceleration, and otherkinematic properties of the target relative to the terrestrial vehicle.A characteristic of a target may include information on the size, shape,orientation, volumetric composition, and material properties, such asreflectivity, material composition, of the target or at least a part ofthe target.

A surrounding environment may be a location and/or setting in which thevehicle may operate. A surrounding environment may be an indoor oroutdoor space. A surrounding environment may be an urban, suburban, orrural setting. A surrounding environment may be a high altitude or lowaltitude setting. A surrounding environment may include settings thatprovide poor visibility (night time, heavy precipitation, fog,particulates in the air). A surrounding environment may include targetsthat are on a travel path of a vehicle. A surrounding environment mayinclude targets that are outside of a travel path of a vehicle. Asurrounding environment may be an environment external to a vehicle.

Referring to FIG. 1, in some embodiments, the radar system 100 maycomprise a front end 102 with two front end apparatuses 10 a and 10 b inwhich at least two phased array modules are arranged perpendicularlywith each other and the received signals are processed by the correlatorof the phased array module. The front end apparatuses 10 a, 10 b may beoperatively connected to a signal analysis module 101 such that theprocessed data (e.g., post correlated data) may further be processed bythe signal analysis module 101 for object recognition, constructingpoint cloud image data and other analysis. In some embodiments, a phasedarray module of the front end apparatuses 10 a, 10 b may comprise atransmit logic 12, receive logic 14 and correlation logic 16 illustratedin FIG. 1. The phased array module and SERDES may include thosedescribed in U.S. Pub. No. 2018/0059215 entitled “Beam-FormingReconfigurable Correlator (Pulse Compression Receiver) Based onMulti-Gigabit Serial Transceivers (SERDES)”, which is incorporated byreference herein in its entirety.

For example, the transmit logic 12 may comprise componentry of the typeknown in the art for use with radar systems (and particularly, forexample, in pulse compression radar systems) to transmit into theenvironment or otherwise a pulse based on an applied analog signal. Inthe illustrated embodiment, this is shown as including a power amplifier18, band pass filter 20 and transmit antenna 22, connected as shown oras otherwise known in the art.

The receive logic 14 comprises componentry of the type known in the artfor use with RADAR systems (and particularly, for example, in pulsecompression RADAR systems) to receive from the environment (orotherwise) incoming analog signals that represent possible reflectionsof a transmitted pulse. In point of fact, those signals may ofteninclude (or solely constitute) noise. In the illustrated embodiment, thereceive logic includes receive antenna 24, band pass filter 26, lownoise amplifier 28, and limiting amplifier 30, connected as shown or asotherwise known in the art.

The correlation logic 16 correlates the incoming signals, as receivedand conditioned by the receive logic 14, with the pulse transmitted bythe transmit logic 12 (or, more aptly, in the illustrated embodiment,with the patterns on which that pulse is based) in order to find when,if at all, there is a high correlation between them. Illustratedcorrelation logic comprises serializer/deserializer (SERDES) 32,correlator 34 and waveform generator 36, coupled as shown (e.g., bylogic gates of an FPGA or otherwise) or as otherwise evident in view ofthe teachings hereof.

FIG. 2 illustrates an example embodiment of a front end 102 for amillimeter wave radar system 100. A millimeter wave radar may emit a lowpower millimeter wave operating at 76-81 GHz (with a correspondingwavelength of about 4 mm). The radar system can also operate at otherfrequency range that is below 76 GHz or above 81 GHz. The radar systemmay comprise any one or more elements of a conventional radar system, aphased array radar system, an AESA (Active Electronically Scanned Array)radar system, a synthetic aperture radar (SAR) system, a MIMO(Multiple-Input Multiple-Output) radar system, and/or a phased-MIMOradar system. A conventional radar system may be a radar system thatuses radio waves transmitted by a transmitting antenna and received by areceiving antenna to detect objects.

As shown in FIGS. 1-3, each of the front end apparatuses 10 a, 10 b mayinclude phased array modules, i.e., a transmit module and a receivemodule. In a first front end apparatus 10 a, a first transmit module 40a may include a first transmit planar component 41 a and a firsttransmit logic 12 a, and a first receive module 42 a may include a firstreceive planar component 43 a and a first receive logic 14 a. In asecond front end apparatus 10 b, a second transmit module 40 b mayinclude a second transmit planar component 41 b and a second transmitlogic 12 b, and a second receive module 42 b may include a secondreceive planar component 43 b and a second receive logic 14 b.

FIG. 3 shows the transmit planar components 41 a, 41 b and the receiveplanar components 43 a, 43 b isolated from other components. Each of theplanar components 41 a, 41 b, 43 a and 43 b may be operatively connectedwith the corresponding phased array logic 12 a, 12 b, 14 a, 14 b byincluding, for example, a slot 44 (FIG. 3) that accommodates thecorresponding phased array logic. While the example embodiment in FIG. 3shows the first transmit planar component 41 a above the second transmitplanar component 41 b, such an arrangement of the planar components mayvary in other embodiments. Moreover, while the example embodiment inFIG. 3 shows the first receive planar component 43 a left of the secondreceive planar component 43 b, such an arrangement of the planarcomponents may vary in other embodiments.

The planar components 41 a/41 b/43 a/43 b may be embodied in the form ofa rectangular substrate or plate, as shown in FIG. 3, and may include afirst end 45 and a second end 46 that are located on oppositelongitudinal ends of the rectangular substrate. The first end 45 of theplanar components 41 a/41 b/43 a/43 b may be operatively connected tothe phased array logic 12 a/12 b/14 a/14 b at the slot 44, and thesecond end 46 of the planar component 41/43 may include an array ofantennas 22 or 24. The phased array logic 12 a/12 b/14 a/14 b mayconnect to the planar component 41 a/41 b/43 a/43 b at the slot 44forming a right angle near the first end 45. The array of transmitantennas 22 and the array of receive antennas 24 may be perpendicular toone another if the transmit planar component 41 a/41 b and the receiveplanar component 43 a/43 b are arranged to be perpendicular to oneanother (FIGS. 2-4).

The planar component 41 a/41 b/43 a/43 b may be formed from a splitblock assembly in that the planar component 41 a/41 b/43 a/43 b isformed by assembling a plurality of blocks. For example, the planarcomponent 41 a/41 b/43 a/43 b may be formed from half blocks 48/49 thatsubstantially mirror one another along a junction plane that divides theplanar component 41 a/41 b/43 a/43 b in half thereby forming twosymmetrical halves. FIG. 4 only shows one of the two half blocks 48/49where the half block 48 is part of the first front end apparatus 10 aand the half block 49 is part of the second front end apparatus 10 b.

The inner surfaces of the blocks of the planar components 41 a/41 b/43a/43 b are formed with recesses or cavities that form the innerstructure of the planar components 41 a/41 b/43 a/43 b as will bedescribed below. The recesses or cavities on the blocks 41 a/41 b/43a/43 b may be formed by a variety of manufacturing methods known in theart (e.g., computer numerical control (CNC) machining, injectionmolding, or the like) capable to achieving desired fabricationtolerances. As shown in FIGS. 5-6, some curved surfaces (i.e., chamfers)may remain on the planar components 41 a/41 b/43 a/43 b due to thenon-zero diameter of the end bit of the CNC milling machine which may be20 mils, for example.

The planar component 41 a/41 b/43 a/43 b may be made of metals (e.g.,aluminum), metallic alloys, thermoplastics, other materials known in theart, or a combination thereof. For example, the planar component 41 a/41b/43 a/43 b may be made of thermoplastics primarily, and be plated orcoated with metals (e.g., gold) or metallic alloys to reduce weight.

In some embodiments, a phased array module 40/42 may include a phaseshifting network in the RF front-end device. In some embodiments, thephase shifting network may be implemented using a Rotman lens 23 (FIGS.1 and 4) which may be interposed between the phased array logic (thetransmit logic 12 or the receive logic 14) and the array of multipletransmit antennas 22/24, as shown in FIG. 1. In some cases, the RFfront-end device may comprise a phase shifting network (i.e., the Rotmanlens 23) and a linear antennas array.

The transmit antennas 22 and/or the receive antennas 24 can be anysuitable type of antennas. For example, the antennas 22/24 may be amicrostrip patch array, Vivaldi antennas, slot coupled patches, hornsand others. In some embodiments, the antennas 22/24 may be microstripbipodal vivaldi antennas that are fed by the Rotman lens 23. Forexample, the antennas array may be coupled to the array ports of theRotman lens 23 on a one-to-one basis.

As shown in FIG. 4, the Rotman lens 23 may include a cavity space 50,and a perimeter of the cavity space 50 may include a first side, asecond side that is opposite the first side, a third side, and a fourthside that is opposite the third side. Input ports or beam ports 50 a maybe located on the first side while output ports or array ports 50 b maybe located on the second side of the cavity space 50. The Rotman lens 23may be configured such that the beam ports 50 a are near the first end45 of the planar component 41 a/41 b/43 a/43 b while the array ports 50b are near the second end 46 thereof.

If one of the beam ports 50 a is excited, the electromagnetic waves willbe emitted into the cavity space 50 and will reach a corresponding oneof array ports 50 b. The shape of contour with the array ports 50 b andthe length of waveguides 52, which connect the ends 45, 46 of the planarcomponent 41 a/41 b/43 a/43 b and the ports 50 a/50 b, are determined sothat, a progressive phase taper is created on the array antennas 22/24and thus a beam is formed at a particular direction in the space.

In the present embodiment, the Rotman lens 23 for the transmit modulehas 63 beam ports and 72 array ports, while the Rotman lens 23 for thereceive module has 30 beam ports and 72 array ports. Moreover, the frontend apparatuses 10 a, 10 b has an azimuth scanning angle of 50 degreesand an elevation scanning angle of 40 degrees. These values may varydepending on how the Rotman lens 23 is embodied. Moreover, the front endapparatuses 10 a, 10 b may include 72 transmit antennas and 72 receiveantennas where the antennas 22, 24 are equidistantly spaced apart fromone another.

The Rotman lens 23 may serve as a robust and low-cost broadband phaseshifting network for the disclosed RF front-end devices and structures.In these cases, active circuitry may be integrated with the beam portsof the Rotman lens, and the lens itself may then be optimized to provideaccurate phasing. In accordance with another aspect of the disclosure,some embodiments may include a Rotman lens 23 with enhanced focusingfunctionality to provide the phasing with low power loss.

The third side and the fourth side of the Rotman lens 23 may includedummy ports or sidewall absorbers 50 c, 59 d, such as radio frequencyabsorbers, are formed to suppress reflections from the sides of theRotman lens 23. The radio frequency absorbers may be made of waveabsorbing materials such as Eccosorb® MCS, LS26 or BSR.

FIGS. 4 and 11 illustrate embodiments of the Rotman lens 23 with jaggedsidewall absorbers 50 c, 59 d. Sidewall absorbers 50 c, 59 d havingshapes shown in FIG. 11 may be effective at attenuating the wavefront ofthe incident pulses. The shape of the sidewall absorbers 50 c, 59 d mayinclude a plurality of sharp triangular “teeth.” As shown in FIG. 14,these triangular teeth 64 may be formed such that the imaginary lines 62extending between adjacent vertices of the triangular teeth 64 pointinginto the cavity space 50 of the Rotman lens 23, may be oriented to besubstantially normal to the curvature of the wavefront. Under such aconfiguration, a substantial amount of energy may be captured in-betweenthe teeth 64 thereby allowing for an effective dissipation by thesidewall absorbers 50 c, 59 d, as observable in FIG. 14.

The properties of a sidewall absorber 50 c/59 d may be tested on afixture 66 a simulated embodiment of which is illustrated in FIG. 12.The properties of a sidewall absorber 50 c/59 d may be tested on thefixture 66 by feeding a signal into the fixture through its inputwaveguide port and measuring the reflection coefficient S11 on a NetworkAnalyzer with waveguide millimeter-wave test heads, a simulatedembodiment of which is illustrated in FIG. 12. Specifically, by emittingwaves through the slot 68 towards the triangular teeth 64 of a sidewallabsorber 50 c/59 d secured in a depression of the fixture 66 andmeasuring the amount of reflection from the triangular teeth 64, it ispossible to test the effectiveness of the sidewall absorber 50 c/59 d.

As shown in FIG. 10, the Rotman lens 23 can be implemented usingwaveguides, microstrip, stripline technologies or any combination ofthese features. In some embodiments, the Rotman lens may bemicrostrip-based Rotman lens. In some embodiments, the Rotman lens 23may be a waveguide-based Rotman lens. In some cases, waveguides may beused in place of transmission lines.

In the embodiment of FIGS. 4-9B, the planar component 41 a/41 b/43 a/43b further includes waveguides 52 between the first end 45 and the beamports 50 a (i.e., first waveguides 52 a) and between the array ports 50b and the second end 46 (i.e., second waveguides 52 b). The waveguides52 may be embodied as rectangular waveguides integrated into the planarcomponent 41 a/41 b/43 a/43 b such that the waveguides 52 form wallsthat guide the propagation of electromagnetic waves through the planarcomponent 41 a/41 b/43 a/43 b during transmission or reception ofantenna signals from the first end 45 to the second end 46 or viceversa.

Each of the waveguides 52 may provide a hollow space through which theelectromagnetic waves propagate. While FIGS. 5-6 show only one half ofthe hollow space of the waveguides 52, the hollow space of the halfblocks 48/49 may form an enclosed space that extends along the planarcomponent 41 a/41 b/43 a/43 b and may take on various geometries toaffect the polarization of the waves at different locations of the frontend apparatus 10 b, 10 b. Specifically, the shape of the cross-sectionof the hollow space may be described based on a reference rectangularcross-section 54 with a given width in the width directions and a givenheight in the height directions. The waveguide 52 may include a sectionwhere the cross-section of the hollow space is as large as the referencerectangular cross-section 54 or smaller than the reference rectangularcross-section 54 as will be described below.

Each of the waveguides 52 of the Rotman lens 23 may be configured toinclude one or more polarization rotators 56 to control the polarizationof the waves out of and into the phased array logics. FIGS. 5-6 show anexample embodiment of the polarization rotator 56 that is integratedonto the waveguides 52. The polarization rotator 56 may include a firstsection 56 a, an iris section 56 b, and a second section 56 c which arecontinuously arranged in a longitudinal direction of the planarcomponent 41 a/41 b/43 a/43 b.

FIG. 5 shows an inner side of a half block 48 of the transmit planarcomponent 41 a/41 b where the polarization rotator 56 is formed near thefirst end 45. The polarization rotator 56 may be similarly formed nearthe first end 45 of the receive planar component 43 a/43 b. In the firstsection 56 a of the polarization rotator 56 (FIGS. 7A-7B), the waveguide52 may include a first set of cuboid obstructions 58 a that protrudeinto the hollow space in opposite height directions such that the heightof the cross-section of the first section 56 a is less than the givenheight of the reference rectangular cross-section 54 while the width ofthe cross-section of the first section 56 a may be the same as the givenwidth of the reference rectangular cross-section 54. Such height andwidth may be substantially constant throughout the first section 56 a inthe longitudinal directions.

In the iris section 56 b of the polarization rotator 56 (FIGS. 8A-8B),the waveguide 52 may include a diagonal set of cuboid obstructions 58 bthat protrude into the hollow space from diagonally opposite corners ofthe reference rectangular cross-section 54 such that an octagonal,cross-sectional area of the iris section 56 b is obtained. Thiscross-sectional area of the iris section 56 b may be substantiallyconstant throughout the iris section 56 b in the longitudinaldirections.

It should be noted that FIG. 8A shows a cross-section across the irissection 56 b of the polarization rotator 56 observed from the viewpointof the first section 56 a such that the second section 56 c is visiblebehind the iris section 56 b while FIG. 8B shows a cross section acrossthe iris section 56 b of the polarization rotator 56 observed from theviewpoint of the second section 56 c such that first section 56 a isvisible behind the iris section 56 b.

In the second section 56 c of the polarization rotator 56 (FIGS. 9A-9B),the waveguide 52 may include a second set of cuboid obstructions 58 cthat protrude into the hollow space from opposite width directions suchthat the width of the cross-section of the second section 56 c is lessthan the given width of the reference rectangular cross-section 54 whilethe height of the cross-section of the second section 56 c may be thesame as the given height of the reference rectangular cross-section 54(FIG. 9A). Such height and width may be substantially constantthroughout the second section 56 c in the longitudinal directions.

Various dimensions of the iris section 56 b (FIG. 6) can affectdifferent parameters of the radar system. The height 60 a of the cuboidobstructions 58 b in the iris section 56 b can be used to tune totaleffective bandwidth and can affect a balance between bandwidth andcentral band frequency. The length 60 b of the cuboid obstructions 58 bof the iris section 56 b can be used to tune the effective band center.The gap 60 c of the iris section 56 b, which is measured between asidewall of the cuboid obstructions 58 b and a sidewall of the secondsection 56 c, can affect both the bandwidth and insertion loss of thepolarization rotation. In one example embodiment, the height 60 a of thecuboid obstructions 58 b of the iris section 56 b, the length 60 b ofthe cuboid obstructions 58 b of the iris section 56 b, and the gap 60 cof the iris section 56 b may respectively be 0.017 in., 0.094 in., and0.035 in. Moreover, the entire length of the polarization rotator thatis the combined length of the first section 56 a, the iris section 56 b,and the second section 56 c may be less than 2λ where λ is equal to awavelength of the waves traveling through the front end.

The aforementioned dimensions of the iris section 56 b may affect theperformance of the antenna which may be described in terms ofS-parameters (where SNM represents the power transferred from Port M toPort N in a multi-port network), as shown in the graph of FIG. 13. Inone embodiment of the iris section 56, the dimensions of the irissection 56 b may control the locations of a minima of S11 (minimumreflection) and a maxima of S21 (maximum transmission) as well as thebeamwidth. In the example of FIG. 13, S11 has a minima of about−31.019899 dB at 78.5 GHz while S21 has a maxima of about −0.00099132481dB.

Due to the complex interaction of the tuning parameters, a systematictuning approach to getting the needed bandwidth, central frequency andinsertion loss are needed when designing the polarization rotator 56.The process for tuning should be to pick nominal values for the threeaforementioned parameters. Nominal values are based on the waveguide 52selected and are typically ¼ to 1 times the waveguide long dimensiondepending on the parameter. Once nominal values are chosen length forthe iris section should be tuned to achieve the needed central frequencyresponse. After central frequency response is achieved, the height ofthe cuboid obstruction 58 b should be tuned to get the desired bandwidthand insertion loss. If bandwidth and insertion loss are not achieved,the gap of the iris section 56 b can be changed to help insertion loss.The gap of the iris section should typically be 30-50% of the longdimension of the waveguide 52. Deviations from this lead to very narrowbandwidths or high insertion loss. Once the desired insertion loss andbandwidth are achieved a re-tune of the length of the iris section willshift the central frequency back to the desired position from the shiftdue to adjustments to parameters such as the height of the cuboidobstructions 58 b and the gap 60 c of the iris section 56.

As shown in FIG. 4, the waveguides 52 extending between the first end 45and the beam ports 50 a of the Rotman lens 23 may form a set of firstwaveguides 52 a in the transmit planar component 41 a/41 b and thereceive planar component 43 a/43 b. Each waveguide in the set of firstwaveguides 52 a may further include one or more polarization rotator(s)56. As further shown in FIG. 4, the waveguides 52 extending between thesecond end 46 and the array ports 50 b of the Rotman lens 23 in thetransmit planar component 41 a/41 b and in the receive planar component43 a/43 b may form a set of second waveguides 52 b. Each waveguide 52 inthe set of second waveguides 52 b in the transmit planar component 41a/41 b and the receive planar component 43 a/43 b may further includeone or more polarization rotator 56.

In the present embodiment of the first front end apparatus 10 a, whichincludes the first transmit planar component 41 a and the first receiveplanar component 43 a, each first waveguide 52 a in the first transmitplanar component 41 a and the first receive planar component 43 a mayinclude a first polarization rotator 56A where the first section 56 a ofthe first polarization rotator 56 is located nearer the first end 41 athan the second section 56 c thereof. Moreover, in the presentembodiment of the first front end apparatus 10 a, each second waveguide52 b in the first transmit planar component 41 a may include a secondpolarization rotator 56B which is positioned adjacent the array ofantennas 22 and in which the first section 56 a of the polarizationrotators 56 is nearer the second end 46 than the second section 56 cthereof. Furthermore, in the present embodiment of the first front endapparatus 10 a, each second waveguide 52 b in the first receive planarcomponent 43 a does not include a second polarization rotator 56B.

In the present embodiment of the second front end apparatus 10 b, whichincludes the second transmit planar component 41 b and the secondreceive planar component 43 b, each first waveguide 52 a in the secondtransmit planar component 41 b and the second receive planar component43 b may also include a first polarization rotator 56A. Moreover, in thepresent embodiment of the second front end apparatus 10 b, each secondwaveguide 52 b in the second receive planar component 43 b may include asecond polarization rotator 56B which is positioned adjacent the arrayof antennas 24 and in which the first section 56 a of the polarizationrotators 56 is nearer the second end 46 than the second section 56 cthereof. Furthermore, in the present embodiment of the second front endapparatus 10 b, each second waveguide 52 a in the second transmit planarcomponent 41 b does not include a second polarization rotator 56B.

In the aforementioned arrangement of polarization rotators 56A and 56B,each of the first front end apparatus 10 a and the second front endapparatus 10 b may include an odd number of sets of polarizationrotators 56A or 56B. Moreover, one of the first front end apparatus 10 aand the second front end apparatus 10 b may include an odd number of setor sets of polarization rotators 56A or 56B in the transmit planarcomponent 41 a or 41 b while the other of the first front end apparatus10 a and the second front end apparatus 10 b includes an even number ofsets of polarization rotators 56A or 56B in the transmit planarcomponent 41 a or 41 b. Specifically, in the present embodiment, each ofthe first front end apparatus 10 a and the second front end apparatus 10b has 3 sets of polarization rotators 56A or 56B. Moreover, the firsttransmit planar component 41 a of the first front end apparatus 10 a mayhave 2 sets of polarization rotators 56A and 56B (one near the first end45 and another near the second end 46) while the first receive planarcomponent 43 a of the first front end apparatus 10 a may have 1 set ofpolarization rotators 56A near the first end 45. In the second front endapparatus 10 b, the second transmit planar component 41 b of the secondfront end apparatus 10 b may have only 1 set of polarization rotator 56Anear the first end 45 while the second receive planar component 43 b mayhave 2 sets of polarization rotators 56A and 56B (one near the first end45 and another near the second end 46).

It should be noted that the total number of sets of polarizationrotators 56A and 56B in the front end apparatus 10 a and the secondfront end apparatus 10 b may vary in other embodiments. For example, thetotal number of sets of polarization rotators 56A and/or 56B in thefront end apparatus 10 a and the second front end apparatus 10 b may be1, 5 or another odd number instead of 3.

The electromagnetic waves propagating through the present apparatus maybe in the Transverse Electric (TE) 10 mode. The polarization of thewaves may be altered by the polarization rotators 56 located throughoutthe first front end apparatus 10 a and the second front end apparatus 10b.

The change in the polarization of waves during propagation through thepresent embodiment of the radar system may be described as follows. Inthe first front end apparatus 10 a, waves originating from the firsttransmit logic 12 a are polarized to be perpendicular to the plane ofthe Rotman lens 23 (FIG. 7B) but undergo a 90-degree polarizationrotation or twist to become polarized parallel to the plane of theRotman lens 23 (FIG. 9B) as the waves propagate through the firstpolarization rotators 56A of the set of first waveguides 52 a of thefirst transmit planar component 41 a in the first front end apparatus 10a. Specifically, the waves move through the first polarization rotator56A (i.e., the first section 56 a, the iris section 56 b and the secondsection 56 c thereof), and the E-plane of the waves is polarized to beparallel to the plane of the Rotman lens 23 of the first transmit planarcomponent 41 a. After the waves move through the Rotman lens 23 of thefirst transmit planar component 41 a, the waves undergo another90-degree polarization rotation or twist at the second polarizationrotators 56B (i.e., the second section 56 c, the iris section 56 b andthe first section 56 a thereof) to become polarized to be perpendicularto the plane of the Rotman lens 23 of the first transmit planarcomponent 41 a and are transmitted from the transmit antennas 22 of thefirst front end apparatus 10 a. If the first transmit planar component41 a is oriented to be horizontal about the ground, the polarization ofthe waves would be vertical relative to the ground out of the transmitantennas 22 of the first front end apparatus 10 a.

As shown in FIGS. 2-4, the linear array of receive antennas 24 isarranged perpendicularly relative to the linear array of transmitantennas 22. Thus, waves from the first transmit planar component 41 athat are reflected by an object return to the receive antennas 24 of thefirst receive planar component 43 a which is perpendicular relative tothe first transmit planar component 41 a. These waves do not go throughpolarization rotators near the second end of the first receive planarcomponent 43 a, and propagate through the Rotman lens 43 of the firstreceive planar component 43 a and through the first polarizationrotators 56A (i.e., the second section 56 c, the iris section 56 b andthe first section 56 a thereof) where the waves become vertical relativeto the plane of the Rotman lens 23 of the first receive planar component43 a. The waves thus reach the first receive logic 14 a of the firstfront end apparatus 10 a at the same polarization relative to the phasedarray logic at which the waves were transmitted from the first transmitlogic 12 a.

In the second front end apparatus 10 b, waves originating from thesecond transmit logic 12 b are polarized to be perpendicular to theplane of the Rotman lens 23 of the second transmit planar component 41 b(FIG. 7B) but undergo a 90-degree polarization rotation or twist tobecome polarized parallel to the plane of the Rotman lens (FIG. 9B) asthe waves propagate through the first polarization rotators 56A of theset of first waveguides 52 a of the second transmit planar component 41b. Specifically, the waves move through the first polarization rotator56A (i.e., the first section 56 a, the iris section 56 b and the secondsection 56 c thereof), and the E-plane of the waves is polarized to beparallel to the plane of the Rotman lens 23 of the second transmitplanar component 41 b. Thereafter, the polarization of the waves remainunchanged during propagation through the rest of the second transmitplanar component 41 b, including through the Rotman lens 23, beforebeing transmitted from the transmit antennas 22 of the second front endapparatus 10 b. If the second transmit planar component 41 b is orientedto be horizontal about the ground, the polarization of the waves wouldchange from vertical to horizontal in the second transmit planarcomponent 41 b.

Thereafter, the receive antennas 24 of the second front end apparatus 10b may detect the waves that were transmitted by the second transmitplanar component 41 b and reflected by an object. The detection of thesewaves may be improved by the fact that the second receive planarcomponent 43 b includes two set of polarization rotators 56A, 56B. Inother words, the waves arriving at the receive antennas 24 may undergoanother 90-degree polarization rotation by the second polarizationrotators 56B of the set of second waveguides 52 b near the second end 46of the second receive planar component 43 b. Specifically, the wavesmove through the first section 56 a, the iris section 56 b and thesecond section 56 c (from FIG. 7B to FIG. 9B) of the second polarizationrotator 56B near the second end 46 and are polarized to become parallelthe plane of the Rotman lens 23 of the receive planar component 43 b (orvertical if the second receive planar component 43 b is positionedvertically with respect to the ground surface). After these detectedwaves propagate through the Rotman lens 23 of the receive planarcomponent 43 b, the polarization of these waves may undergo yet another90-degree polarization rotation at the first polarization rotators 56Aof the set of first waveguides 52 a near the first end 45 of the secondreceive planar component 43 b. Specifically, the waves move through thesecond section 56 c, the iris section 56 b, and the first section 56 a(from FIG. 9B to FIG. 7B) of the first polarization rotators 56A nearthe first end 45 and are polarized to become perpendicular to the planeof the Rotman lens 23 of the second receive planar component 43 b (i.e.,with a horizontal polarization about the ground surface if the secondreceive planar component 43 b is perpendicular to the ground surface).The waves thus reach the second receive logic 14 b at the samepolarization relative to the phased array logic at which the waves weretransmitted from the second transmit logic 12 b.

The expression “90-degree polarization rotation” or other expressionsrelating to rotating the polarization of the waves by “90-degree” or “90degrees” are meant to include rotation by 270 degrees, 630 degrees, orthe like in the opposite rotational direction or rotation by degrees orthe like in the same rotational direction as long as the finally reachedposition can be reached through a rotation by 90 degrees.

In one example arrangement, the transmit module 40 a/40 b and thereceive module 42 a/42 b may be configured in a bi-static manner. Thebi-static configuration may refer to the working configuration where thereceiving module 42 and the transmitting module 40 are separated or notco-located. The illustrated example shows that the vertically arrangedreceive module 42 is configured to be in a receiving mode while thehorizontally arranged transmit module 40 is configured to be in atransmission mode. The bi-static Tx/Rx configuration of the two phasedarray modules may be fixed or switchable. In some cases, the verticalreceive module 42 and horizontal transmit module 40 can be switched suchthat the vertical module is the transmitter and the horizontal module isthe receiver.

If the radar system is in the bi-static Tx/Rx configuration, one or moreparameters of the antenna arrays (e.g., gain, directivity) for thereceiving and transmitting may be different. Similarly, one or moreconfigurations of the Rotman lens or RF absorbers corresponding to one(transmit/receive) front end may be different from those of theperpendicularly arranged (receive/transmit) front end.

The aforementioned arrangement of two front end apparatuses 10 a and 10b in which the two sets of transmitted waves are perpendicular from oneanother may increase the information bandwidth capacity of the radarsystem 100 thereby allowing more information to be obtained about anydetected objects or obstacles and enabling more accurate identificationof these objects or obstacles.

In alternative embodiment (FIG. 10), the front end may feed an array ofmicrostrip patch antennas using microstrip delay-line beamformer. Themicrostrip patch antennas may be fabricated using printed circuit boardtechnologies. The patch antennas are resonant antennas fed by a truetime delay microstrip beamformer without using a lens. An array ofVivaldi antennas may also be connected to the microstrip-based Rotmanlens. This may advantageously provide a device with compact and smallerstructure, improved accuracy and easy fabrication. In an examplereceiving module, the patch antennas may be selected (e.g., by selectingpatch size and location) such that the patch array operates at thecenter frequency which is about 78.5 GHz. In some embodiments, the patcharray may comprise 32 patches. Those skilled in the art will appreciatethat other number of patches that is smaller than or greater than 32 canbe utilized.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed is:
 1. A front end of a radar system comprising: a firstfront end apparatus including a first transmit planar component and afirst receive planar component, the first transmit planar component andthe first receive planar component arranged to be perpendicular to oneanother; and a second front end apparatus including a second transmitplanar component and a second receive planar component, the secondtransmit planar component and the second receive planar componentarranged to be perpendicular to one another, each of the first transmitplanar component, the first receive planar component, the secondtransmit planar component and the second receive planar componentincluding: a first end; a second end located opposite the first end,electromagnetic waves propagating in propagation directions between thefirst end and the second end; a cavity space bounded by beam ports alonga first side of the cavity space and by array ports along a second sideof the cavity space, the cavity space being in operative communicationwith the beam ports and with the array ports to form a Rotman lens; anda linear array of antennas located along the second end of the planarcomponent, each of the antennas being in operative communication with acorresponding one of the array ports, wherein the first transmit planarcomponent and the second transmit planar component are parallel to oneanother, and the first receive planar component and the second receiveplanar components are parallel to one another, and wherein a first setof waves are transmitted from the linear array of antennas of the firsttransmit planar component to be received by the linear array of antennasof the first receive planar component, and a second set of waves aretransmitted from the linear array of antennas of the second transmitplanar component to be received by the linear array of antennas of thesecond receive planar component.
 2. The front end of claim 1, whereinpolarization of the first set of waves transmitted from the linear arrayof antennas of the first transmit planar component and polarization ofthe second set of waves are transmitted from the linear array ofantennas of the second transmit planar component are perpendicular toone another.
 3. The front end of claim 2, wherein each of the firsttransmit planar component, the second transmit planar component, thefirst receive planar component and the second receive planar componentfurther includes a set of first waveguides that extend between the firstend of the planar component and the beam ports, and a set of secondwaveguides that extend between the array ports and the second end of theplanar component.
 4. The front end of claim 3, wherein the set of firstwaveguides and the set of second waveguides in each of the first frontend apparatus and the second front end apparatus include one or moresets of polarization rotators totaling an odd number.
 5. The front endof claim 4, wherein the set of first waveguides and the set of secondwaveguides in the first transmit planar component include one or moresets of polarization rotators totaling an odd number, and the set offirst waveguides and the set of second waveguides in the second transmitplanar component include one or more sets of polarization rotatorstotaling an even number or zero.
 6. The front end of claim 5, whereinthe waves undergo a 90-degree polarization twist while propagatingthrough each set of polarization rotators.
 7. The front end of claim 5,wherein each of the polarization rotators includes a first section, aniris section, and a second section in the longitudinal direction,wherein the first section includes a first set of cuboid obstructionsthat protrude into the hollow space from opposite height directions suchthat the first section of the hollow space has a first rectangularcross-section with a first height and a first width, the first height isless than the given height, the first width is equal to the given width,and the first height and the first width are substantially constantthroughout the first section in the longitudinal direction, wherein theiris section includes a diagonal set of cuboid obstructions thatprotrude into the hollow space from diagonally opposite corners of thereference rectangular cross-section such that a cross-sectional area ofthe iris section of the hollow space is octagonally shaped and isreduced relative to the reference rectangular cross-section, thecross-sectional area of the iris section is substantially constant inthe longitudinal direction, wherein the second section includes a secondset of cuboid obstructions that protrude into the hollow space fromopposite width directions such that the second section of the hollowspace has a second rectangular cross-section in which a second heightand a second width, the second width is less than the given width, thesecond height is equal to the given height, and the second height andthe second width are substantially constant throughout the secondsection in the longitudinal direction.
 8. The front end of claim 7,wherein a gap between one of the cuboid obstructions of the iris sectionand one of the cuboid obstructions of the second section is 30%-50% ofthe given width of the reference rectangular cross-section.
 9. The frontend of claim 7, wherein a length of each of the polarization rotatorspanning the first section, the iris section, and the second section isless than 2λ, λ being equal to a wavelength of the waves travelingthrough the front end.
 10. The front end of claim 1, wherein each of thefirst front end apparatus and the second front end apparatus includes atransmit logic and a receive logic, and each of the transmit planarcomponent and the receive planar component includes near the first end aslot to operatively connect to a correlation logic.
 11. The front end ofclaim 1, wherein each of the first transmit planar component, the secondtransmit planar component, the first receive planar component and thesecond receive planar component is formed from a first block and asecond block, each of the first block and the second block defines asymmetrical half of the hollow space, the first block and the secondblock are joined along a junction plane which splits a thickness of theplanar component in half.
 12. The front end of claim 1, wherein thewaves propagate in a Transverse Electric (TE) 10 mode.
 13. The front endof claim 1, wherein the antennas of the transmit front end apparatus andthe antennas of the receive front end apparatus are in a bi-staticconfiguration.
 14. The front end of claim 1, wherein the linear array oftransmit antennas and the linear array of receive antennas are phasedarrays of antennas.
 15. An autonomous vehicle comprising the radarsystem including the front end of claim
 1. 16. A method of detecting anobject, the method comprising: providing a first linear array oftransmit antennas and a second linear array of transmit antennas, thefirst linear array of transmit antennas and the second linear array oftransmit antennas being parallel to one another; providing a firstlinear array of receive antennas and a second linear array of receiveantennas, the first linear array of receive antennas and the secondlinear array of receive antennas being parallel to one another;arranging the first linear array of transmit antennas and the firstlinear array of receive antennas to be perpendicular to one another;arranging the second linear array of transmit antennas and the secondlinear array of receive antennas to be perpendicular to one another;phase-shifting first waves by propagating the first waves through afirst Rotman lens that is in operative communication with the firstlinear array of transmit antennas; phase-shifting second waves bypropagating the second waves through a second Rotman lens that is inoperative communication with the second linear array of transmitantennas; transmitting the first waves through the first linear array oftransmit antennas; transmitting the second waves through the secondlinear array of transmit antennas; receiving the first waves reflectedby an object through the first linear array of receive antennas;receiving the second waves reflected by an object through the secondlinear array of receive antennas; propagating the first waves reflectedby an object through a third Rotman lens that is in operativecommunication with the first linear array of receive antennas; andpropagating the second waves reflected by an object through a fourthRotman lens that is in operative communication with the second lineararray of receive antennas.
 17. The method of claim 16, whereinpolarization of the first waves transmitted through the first lineararray of transmit antennas and polarization of the second wavestransmitted through the second linear array of transmit antennas areperpendicular to one another.
 18. The method of claim 17, furthercomprising rotating a polarization of the first waves by 90 degrees anodd number of times before the first waves propagate from the firstlinear array of transmit antennas, and rotating a polarization of thesecond waves by 90 degrees an even number of times before the secondwaves propagate from the second linear array of transmit antennas. 19.The method of claim 18, further comprising rotating a polarization ofthe first waves by 90 degrees an odd number of times as the first wavespropagate from the first transmit logic to a first receive logic, androtating a polarization of the second waves by 90 degrees the same oddnumber of times as the second waves propagate form the second transmitlogic to a second receive logic.
 20. The method of claim 16, furthercomprising correlating the first waves from a first transmit logic withthe first waves reflected by an object and correlating the second wavesfrom a second transmit logic with the second waves reflected by anobject.